Field of the Invention
The present invention relates to a wafer processing method for dividing a wafer into a plurality of individual device chips along a plurality of crossing division lines formed on the front side of the wafer, the front side of the wafer being partitioned by the division lines to define a plurality of separate regions where a plurality of devices are formed.
Description of the Related Art
In a semiconductor device fabrication process, a plurality of crossing division lines are formed on the front side of a substantially disk-shaped semiconductor wafer to thereby define a plurality of separate regions where a plurality of devices such as integrated circuits (ICs) and large scale integrations (LSIs) are formed. The semiconductor wafer is cut along the division lines to thereby divide the regions where the devices are formed from each other, thus obtaining individual device chips corresponding to the devices.
As a method of dividing a wafer such as a semiconductor wafer along the division lines, there has been put into practical use a laser processing method called internal processing using a pulsed laser beam having a transmission wavelength to the wafer, wherein the pulsed laser beam is applied to the wafer in the condition where the focal point of the pulsed laser beam is set inside the wafer in an area to be divided. A wafer dividing method using this laser processing method includes the steps of applying a pulsed laser beam having a transmission wavelength to the wafer from one side thereof in the condition where the focal point of the pulsed laser beam is set inside the wafer, thereby continuously forming a modified layer inside the wafer along each division line, and next applying an external force to the wafer along each division line where the strength has been reduced by the formation of the modified layer, thereby breaking the wafer along each division line to divide the wafer into the individual device chips (see Japanese Patent No. 3408805, for example).
Further, a semiconductor wafer intended to improve the processing performance of semiconductor devices such as ICs and LSIs has been put into practical use. This semiconductor wafer is composed of a substrate such as a silicon substrate and a functional layer formed on the front side of the substrate, wherein the functional layer is composed of a low-permittivity insulator film (low-k film) and a functional film formed on the low-k film, the functional film forming a plurality of circuits. Thus, the semiconductor devices are formed from the functional layer. The low-k film is formed from an inorganic film of SiOF, BSG (SiOB), etc. or an organic film such as a polymer film of polyimide, parylene, etc. However, the low-k film is very brittle like mica. Accordingly, in the case of using such a wafer having a functional layer formed on the front side of a substrate such as a silicon substrate, wherein the functional layer includes a low-k film, and then forming a modified layer inside this wafer (substrate) along each division line to apply an external force to the wafer, thereby dividing the wafer along each division line, there arises a problem such that the low-k film may be separated and this separation (delamination) may reach the devices to cause fatal damage to the devices.
Further, known is a wafer having a metal film called test element group (TEG) for testing the function of each device, wherein the metal film is formed on a part of each division line. In the case of forming a modified layer inside such a wafer along each division line and applying an external force to the wafer, there arises a problem such that the devices divided from each other may be connected through the metal film, so that the individual device chips cannot be obtained.
To solve these problems, there has been proposed a processing method such that a laser beam is applied along each division line to perform ablation to the low-k film or the metal film as a stacked member formed on each division line, thereby removing the stacked member.